This invention relates to spraying equipment operated by a gas such as air although other propellants, for example, Freon (trademark) are known. The invention relates particularly, but not exclusively, to airbrushes. Airbrushes are tools used by artists and illustrators for selectively spraying coloured dyes or pigments dissolved or dispersed in an aqueous or other liquid solvent or carrier to form inks, paints or similar media (hereinafter referred to as "paint" for the sake of convenience), and are used extensively in the preparation of advertisements and like commercial artwork, although such is the skill of exponents that airbrush work is now considered a fine art form.
A definitive work detailing the history, the construction and use of airbrushes is "The Airbrush Book" by Seng-gye Tombs Curtis and Christopher dunt published by Orbis Publishing Limited, London in 1980. This reference describes in detail the various types of airbrush past and present. As fine art tools, airbrushes are relatively delicate and, moreover, they are expensive. For example, conventionally, the nozzle and/or the needle (which control the release of paint) are made of brass or stainless steel. They are easily damaged in that, to provide a different sized nozzle, to replace a damaged nozzle or needle or for cleaning purposes, the airbrush must be disassembled, cleaned and reassembled. During reassembly, the needle must be inserted into the nozzle to exactly the correct extent to ensure a seal and to avoid damaging the nozzle.
FIG. 1 is a diagrammatic fragmentary cross-section of a known nozzle/needle combination.
The needle 10 has a tip of substantially conical shape sealingly fitting into a nozzle 12. The aperture in the nozzle 12 may be, for example, 0.2 mm. The diameter of the needle may taper from 1.5 mm to a point.
The angle of taper is small so that, upon retraction of the needle, a large movement is necessary to give an appreciable change in the flow of paint. This is desirable so as to give greater control of paint flow. However, if the angle of taper of the needle is too small, the mechanical advantage is such that on moving to the closed position, the needle tip 11 tends, in use, permanently to spread the nozzle opening. The sealing may be reduced but also the airbrush no longer has the required control characteristics in the dispensation of paint. If the needle is bent, the paint will not flow evenly. If the nozzle is bent or distorted, it will not locate concentrically with the needle or a surrounding air cap 13 and the air flow through the annulus between the nozzle and the air cap will be uneven. Uneven flow of paint or of air gives rise variously to spatter or spitting. In an extreme case, of course, the nozzle 12 may well be split or cracked by the needle tip 11.
The needle and the nozzle are both relatively expensive items to replace but the errors produced due to these faults and the time lost in replacement or cleaning can be more expensive.
Other forms of spraying equipment utilise concentric needle, nozzle and air cap arrangements and, to varying extents, suffer from the disadvantages above ascribed to airbrushes. The present invention relates equally to such spraying equipment.
The nozzle and the needle/nozzle unit described hereinafter form the subject matter of my copending patent application Ser. No. 06/948,357 filed simultaneously herewith and claiming priority from my UK patent application No. 8507966 filed Mar. 27, 1985.
"Double independent control" of air and paint is provided by a single operating member in most high class commercially available airbrushes. The operating member is depressed to increase the flow of air and is moved in a second substantially perpendicular direction, usually rearwardly, to control the retraction of the needle and thereby the flow of paint.
FIG. 2 of the accompanying drawings is a fragmentary diagrammatic sketch of a prior art airbrush air and needle control means.
A manually operated control means comprises a button 14 depressable to move a rod 15 pivotally connected thereto whereby progressively to open an air valve (not shown). The rod slides in an aperture of the body member 17. The button stem 16 is bifurcated to straddle the needle 10. The body member 17 provides a fulcrum 18 whereabout a lever 19 may pivot. The lever 19 engages a needle support 20 and thereafter is curved forwardly to form a sliding engagement with the stem 16. Pivotal movement of the stem 16 in a clockwise direction (as seen in the drawings) pivots the lever 19 about its fulcrum and urges the needle support 20 and hence the needle 10 to the right. The needle is thereby retracted in the nozzle (not shown) to dispense the paint. The arrangement constitutes an approximately 1:4 linkage and the movement of the needle 10 corresponds substantially linearly to that of the button 14. Such movement does not give rise to the desired initial finest control mentioned above.
In my copending application Ser. No. 06/948,357 filed simultaneously herewith, the problems arising from the limitations of the nozzles are solved. Maximum advantage of this solution can only be achieved, however, if the control of the dispensation of both air and paint is also optimised. Thus, for finest control, it is essential that at least the initial movement of the needle, upon retraction, be effected with the utmost accuracy and precision.
An object of the present invention is the provision of an improved control means for a gas-operated spraying apparatus wherein the aforesaid optimisation is realized.